Fig. 5.

Distortions of scalp amplitude and phase during phase-locked states as revealed by forward modeling. (A) Shows that amplitude at the electrodes is affected by the relative phase between sources and their proximity. For distant sources (p = 0), scalp amplitude is undisturbed as a function of relative phase (rear of surface, annotated 1). For closely located sources, amplitudes with relative phase close to inphase are overestimated (amplitude summation) and underestimated for antiphase (attenuation). For p = .95, there is complete cancellation of scalp signals from sources antiphase and maximal amplitude enhancement inphase (front of surface, annotated 2). (B) Shows that relative phase at the scalp is affected by relative phase between sources and their proximity. For distant sources, relative phase between the electrodes is undistorted (diagonal line annotated 3 on the left of the surface). As proximity between sources increases, relative phases appear close to inphase at the scalp. Eventually, for p = .95, any relative phase between the sources shows up in the scalp as inphase (horizontal line annotated 4 on the right of the surface). A singularity exists at antiphase: scalp relative phase is preserved for any value of p except p = .95 at which phase is not defined.